Better BuildCurves3d_s parameters in makeHelix

[adam-urbanczyk]

This will resolve #385 . The parameters are chosen "experimentally", so future changes are possible.

[codecov]

Codecov Report

Merging #387 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #387   +/-   ##
=======================================
  Coverage   93.31%   93.31%           
=======================================
  Files          19       19           
  Lines        4847     4847           
  Branches      483      483           
=======================================
  Hits         4523     4523           
  Misses        210      210           
  Partials      114      114           

Impacted Files	Coverage Δ
cadquery/occ_impl/shapes.py	90.15% <100.00%> (ø)

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[adam-urbanczyk]

I think this PR can be merged @jmwright . Current settings produce a correct result for at least 1000 turns:

import cadquery as cq

R = 500 # helix radius
N = 1000 # helix turns - incorrect output for N > 42
P= 10 # helix pitch

w = cq.Wire.makeHelix(pitch=P, height=N*P, radius=R)
show_object(w)

I think this is enough for a typical user. In the future we might want to assemble the final helix form multiple edges.

[jmwright]

Thanks @adam-urbanczyk , merging.